The weird devices on the walls of women’s bathroom stalls in Japan have been around at least since March of 2003, and I believe I saw some in 2001, but Yahoo! News: Oddly Enough has only recently picked up on it.
I kept setting it off by accident in the bathroom of the Hiroshima Peace Memorial Museum. What’s making that canned flushing noise? I’d wonder, frantically twisting around. Finally I spotted the motion sensor, right next to my left arm. Even after finding it I couldn’t help but set it off, so I gave up and let it keep making noise.
At the time, I had no idea what its use was, and I kept wondering if I was messing something up. It was only later that the thought occurred to me that it might be there for privacy.